Referring to FIG. 1, a traditional BBS (base station subsystem) consists of a base transceiver station (BTS), a base station controller (BSC), a packet service server (MFS), and a TC (transcoder). It is externally connected to a mobile switching center (MSC) through the TC and wirelessly to a mobile terminal (MS) through the BTS. Within this system, transmissions are all based on a TDM (time division multiplexing) mode, and there is no distinction between a control plane and a user plane. For the BSC, its external interfaces involve ABIS interfaces from the BTS and Ater interfaces from the TC; for the TC, its external interfaces involve A interfaces with the MSC.
Compared with the traditional TDM network outlined above. IP networks are already well developed and need a low cost for operation maintenance. Therefore, it is an inevitable trend in the telecommunication industry that various transmission networks merge into IP networks.
However, how to cope with issues, such as BIS management in different transmission modes, call handover between BTSs operating in different operation modes or the like in the course of TDM networks merging into IP networks, has been a research task to which this industry and the applicant are denoted.